The invention relates to a voltage regulator for a generator, drivable by an internal combustion engine.
It is known that when strong electrical consumers in an on-board motor vehicle electrical system are turned on, the generator is put under a heavy load. Since turning on such an electrical consumer causes a voltage collapse, the voltage regulator, by increasing the exciter current, seeks to increase the power output by the generator and to keep the output voltage of the generator essentially constant. As a result of proceeding in this way, the braking moment caused by the generator, which finally acts on the engine crankshaft, is increased, so that at low engine rpm, and especially during idling, an rpm collapse can occur.
To keep such an rpm collapse when strong electrical consumers are turned on as low as possible, in voltage regulators for generators in motor vehicles, provisions are made that are known by the term xe2x80x9cload responsexe2x80x9d.
In voltage regulators with a xe2x80x9cload-response functionxe2x80x9d, the exciter current after a strong consumer is turned on is increased not suddenly but rather continuously. For detecting the load turn-on, the ON duration of the regulating transistor is for instance evaluated. A voltage regulator for an internal combustion engine-driven generator that has both a load-response function and the evaluation of the exciter current duty factor is known for instance from German Published, Unexamined Patent Application DE-OS 196 38 357.
Another voltage regulator for an internal combustion engine-driven generator, which also has a limitation of the rise of the exciter current after a load turn-on, is known from European Patent Application 0 496 185 A1. In this known voltage regulator, both the actual value of the generator output voltage and the actual value of the exciter current are detected. As a function of these two detected values, a voltage regulation takes place that on the one hand keeps the rise in the exciter current after an electrical load has been turned on within predeterminable limits and on the other shifts these limits if the actual value of the generator output voltage drops off too sharply.
Both the known versions have the disadvantage that in the voltage regulator known from DE-OS 196 38 357 the reaction takes place only after a certain time, specifically not until the current rise has already occurred, while in the voltage regulator known from EP 0 496 185 A1, additional means are needed that detect the exciter current, and these means entail considerable expense in terms of circuitry for the sake of the requisite precision.
The voltage regulator according to the invention for a generator drivable by an internal combustion engine, having the characteristics of claim 1, has the advantage that the limitation in the exciter current rise rate after a strong electrical consumer is turned on is effected immediately, without requiring complicated means for measuring the exciter current. These advantages are obtained in that, in a voltage regulator the closed-loop control circuit for the exciter current is designed such that it includes a system with a digital pulse width modulator, which regulates the pulse width ratio as a function of the detected output voltage of the generator, and superimposed on this regulation is also a damping, which brings about an overriding turn-off of one period of the signal furnished by the pulse width modulator.
By means of this kind of voltage regulator, a regulation of the generator output voltage is attained that has high stability and leads to a regulated voltage with only very slight residual waviness. The so-called xe2x80x9cload responsexe2x80x9d, that is, the reaction to a load turn-on, can be compensated for in an especially advantageous way, which even makes it possible to reduce the exciter current rise rate to arbitrary values.